Non-volatile memory (NVM) devices are commonly used in the electronics world and provides computer memory that can retrieve stored information even when not powered. Non-volatile memory cells include floating gate transistors and in some cases, split-gate floating gate transistors. Non-volatile memory cells typically include an array of floating gate transistors and some adjacent floating gate transistors are isolated and separated from one another using thick oxide structures. The thick oxide structures include shallow trench isolation (STI) devices formed in trenches and filled with dielectric materials, and also thick field oxide, FOX, structures disposed between the transistors.
The STI or FOX structures used to separate and isolate adjacent floating gate transistors from one another generally include upper surfaces that extend above the substrate surface and which form sharp interfaces with the substrate surface. This topography can cause several problems including the undesirable retention of charge at undesired locations. The etching processes used to form trenches within which the STI structures are formed, create undesirable crystal defects in the sidewalls of the trenches. The STI or FOX structures have been found to be the source of stress defects, electrical defects and poor topography that causes degradation of NVM performance. It would be desirable to produce NVM cells without the above-identified problems.